Previous methods for obtaining this dienamine have generally required two separate steps, one being amination, the second being isomerization. Usually the product of the amination was isolated and followed by catalytic isomerization. In the two-step method, the starting material, for example, myrcene or isoprene, was converted to the corresponding terpenyl amine, e.g., geranylamine (See Fujita et al, Chem. Ind. (London), 231 (1973) or nerylamine, as the case might be. The terpenylamine was recovered and then isomerized in a separate medium using an expensive catalyst. In the case of the nerylamine, for example, the catalyst was an alkali metal 2-aminoethylamide in ethylenediamine (See Tanaka et al, Chem. Ind. (London) 202 (1977)). Alternatively, the prior art utilized a cobalt catalyst with both geranylamine and nerylamine, which gave the dieneamine as a minor by-product. Use of either type of catalyst, however, involved considerable expense and long reaction times to make the desired dienamine.
A method for bringing about the isomerization of an allylic amine to an enamine has been reported (E. A. Zuech, R. F. Kleinschmidt, and J. E. Mahan, J. Org. Chem., 31, 3713 (1966)). The method describes the addition of the primary amine to a butadiene which is followed by the isomerization of the resulting amino-substituted butenyl anion. The mechanism proposed to accomplish the shift of the double bond toward the amino-substituted group is regeneration of the methylamide base. In contact with this strong regenerated base, the 2-butenyl derivative becomes a 1-butenyl compound, reflecting the shift of the double bond one carbon atom closer to the amino-substituted group.
The present process differs from Zuech's proposed route in a number of ways. First, the amine addition compound undergoing isomerization, i.e., shift of the double bond, has at least two double bonds present. Additionally, the shift of the double bond is experienced over a distance of more than one carbon atom and into a conjugate relationship, instead of the one-carbon atom shift contemplated by the Zuech reference. The starting material myrcene or alkyl or alkenyl substituted myrcene is at least a triene. Also the Zuech reference describes double bond migration in a secondary amine system, which contains an acidic proton on nitrogen, and not a tertiary amine system. Finally, the resulting compound in the present process becomes a conjugated diene or a dienamine instead of an enamine. The Zuech reference of course is not a conjugated compound because there is only one double bond present in the product.
Hata et al, Japanese Kokai No. 70707/76 (1976) have shown the reaction of myrcene with a dialkylamine in the presence of a lithium catalyst (liquid phase) to produce geranylamine, not the tertiary dienamine obtained in accordance herewith.
G. T. Martirosyan and others have published several studies relative to reactions of diene hydrocarbons with dimethyl amine (1:1) in the presence of alkali metal. Isoprene was reacted with dimethyl amine in the presence of sodium in benzene to give in high yield (82%) an allylic tertiary amine (CA 59, 6354d (1963)). Dimethyl amine was added to butadiene by introducing the latter into the amine in benzene at 25.degree. C. in the presence of sodium. Again, an allylic tertiary amine was obtained in high yield (81.6%). The amine was present in excess. (CA 62, 11810e (1965)). In another study, the authors passed the dimethyl amine through the conjugated unsaturate (isoprene) in diethyl ether solution in the presence of sodium over 24 hours gave a 70% yield of allylic tertiary amines. (CA 63, 14686b (1965)). Studies were made at 2.degree.-4.degree. C. and 45.degree.-50.degree. C. in reacting isoprene with dimethyl amine in the presence of sodium. It was determined that at higher temperatures, enamine was formed in significant amount. At lower temperatures small amounts of enamine were found. (CA 68, 38968p (1968)). The catalytic activity of Li or K was found to be less effective than Na in the amination of isoprene with dialkyl amine (CA 68, 86981 u (1968)).
Noren, J. Org. Chem. 40, 967 (1975) investigated the effects of various alkali metal catalysts in dialkyl amine additions to isoprene to give 1,4- and 4,1-addition products. Some isomerization was noted at relatively low temperatures (0.degree. to 30.degree. C.).
We have found that the desired tertiary dienamine can be made in a single step, and that the reaction time for the single step can sometimes be shorter than one hour. In addition, the expensive catalysts used to bring about the isomerization in the two-step process have been found to be unnecessary. One less expensive alkali-metal catalyst can be used in the present invention for both amination and isomerization. A one-step process is described wherein the starting polyene and the dialkylamine are both maintained in a liquid phase and in the same vessel for both amination and isomerization. Contrary to much of the prior art, the dialkylamine or secondary amine is utilized in a quantity in excess of stoichiometric relative to the myrcene. Also present is a Group Ia catalyst. The advantage of the present process is clear in view of the use of a less expensive catalyst, as well as ability to make a useful product in a single step without isolation of intermediate or change of medium instead of two or more steps. The product is recoverable by distillation. Yields of the desired product are often in the range of around 40 to 65%. Surprisingly, it is the isolated double bond in the myrcene nucleus that moves into conjugation to form the dienamine. This has not previously been found so far as we have been able to determine.